diff --git a/skimage/measure/_regionprops.py b/skimage/measure/_regionprops.py
index 71da3c1a..69710c87 100644
--- a/skimage/measure/_regionprops.py
+++ b/skimage/measure/_regionprops.py
@@ -570,7 +570,7 @@ def perimeter(image, neighbourhood=4):
     perimeter_weights[[13, 23]] = (1 + sqrt(2)) / 2
 
     perimeter_image = ndimage.convolve(border_image, np.array([[10, 2, 10],
-                                                               [ 2, 1, 2],
+                                                               [ 2, 1,  2],
                                                                [10, 2, 10]]),
                                        mode='constant', cval=0)